Neutrino-excitation of baryon resonances and single pion production

This is an attempt to describe all existing data on neutrino production of single pions in the resonance region up to W = 2 GeV in terms of the relativistic quark model of Feynman, Kislinger and Ravndal (FKR). We considered single pion production to be mediated by all interfering resonances below 2 GeV. A simple noninterfering, nonresonant background of isospin $\text{1}\text{2}$ was added. It improved agreement with experiment, particularly in the ratio of isospin amplitudes in charged current reactions, at the expense of one additional constant. All total cross sections, cross section ratios and W-distributions are well reproduced at low and high energies, with charged and neutral currents (supposing the Salam-Weinberg theory with sin²$\text{θ}{}_{\mathrm{w}}\text{≈}\text{1}\text{4}$ to be correct), and for neutrinos and antineutrinos, giving predictions where data are lacking. New predictions have been made for complex angular distributions in $\text{N}$π channels exhibiting strong interference between neighbouring resonances. These are sensitive (for 1.1 GeV ? W ? 1.5 GeV) to the sign of the Roper resonance P₁₁(1450) which is controversial in photoproduction experiments.     

Observation of charmed baryon production in νp interactions in BEBC

Two examples of charmed baryon production by neutrinos have been observed in BEBC filled with hydrogen. Both events fit uniquely the reaction νp → μ^?pK^?π⁺π⁺ and thus apparently violate the ΔS = ΔQ rule. None of the appropriate mass combinations is consistent with the mass values of the D⁰ and D⁺ mesons. However, for the mass combinations of the pK^?π⁺ systems, values of (2.285 ± 0.005) GeV and (2.280 ± 0.003) GeV are found for event 1 and 2, respectively. These values agree with the mass of (2.285 ± 0.006) GeV for the Λ_c⁺ charmed baryon determined recently in e⁺e^? collisions at SLAC.     

Exploring the doubly charmed baryon

The doubly charmed baryon,like the proton and neutron,is formed by three quarks.However,they are different,as such a baryon consists of two heavy quarks(charm-quark)and one light quark,while the proton and neutron respectively contain three light quarks.Therefore the doubly charmed baryon is expected to have different internal structures and properties.For example,its mass is 3-4 times higher than those of the proton and neutron.Studying the doubly charmed baryons can provide important information to understand the three-body bound system,the hadronic interaction and the quark model.     

Photoexcitation of baryon resonances

The study of baryon resonances via meson photoproduction reactions on the free proton, nucleons bound in light nuclei, and in the nuclear medium is discussed. Special emphasis is laid on the production of neutral mesons which due to the suppression of non-resonant backgrounds are particularly well suited for the study of excited states of the nucleon. Experiments carried out during the last ten years with the TAPS-detector at the Mainz MAMI accelerator have contributed very significantly to the detailed investigation of the four lowest lying baryon resonances the P₃₃ (1232), the P₁₁ (1440), the D₁₃(1520) and the S₁₁(1535). Future experiments with TAPS at the ELSA accelerator have a large potential for the investigation of higher lying resonances via many different decay channels.     

Hunting the doubly charmed baryon with strangeness

正In the standard model of particle physics, the baryon is formed by three quarks. Unlike the well-known proton and neutron that are composed of three light quarks, the doubly charmed baryon consists of two heavy charm quarks and a light quark.Therefore, it is expected to have different internal structures and properties, and to serve as a unique system for understanding the three-body bound system and testing the mechanism of quantum chromodynamics (QCD).     

Dispersion theory relations and charmed baryon couplings

Dispersion theory sum rules proposed by Atkinson have been obtained for the invariant amplitudes of the elastic pion-charmed baryon scattering process. Saturating the sum rules with the known intermediate states, we obtain the pion-charmed baryon coupling constants.     

Diffractive production of the charmed baryon Λ+c at the CERN ISR

In a sample of diffractive events of high multiplicity a sharp five standard deviation signal is observed at M = 2255 MeV/c² in the K^?pπ⁺ mass distribution and, although with less statistical strength, at the same mass in the Λ⁰π⁺π⁺π^? channel. These signals are identified as being due to the decay of the charmed baryon Λ⁺_c which is produced with a cross section times branching ratio σ_cB in the range 0.7?1.8 μb for the K^?π⁺p decay and 0.3?0.7 μb for the Λ^-π⁺π⁺ π^? system.     

Weak decays of charmed baryons

We use the quark model framework to calculate the weak decays of the lowest lying charmed baryons into ground state baryons and mesons. We present detailed results on the predicted flavour and multipole composition of the final state configurations which can be tested in the near future. For the decays 1/2⁺→1/2⁺+0^? we also give symmetry and current algebra estimates which we compare with the quark model results. Semileptonic branching ratios in charmed baryon decays are calculated to be of the order of ～5%. The total lifetime of charmed baryons is predicted to be ～7 10^?14 s which is 5–10 times smaller than the free quark model estimate.     

Dilepton decays of baryon resonances

Dalitz decay of baryon resonances is studied and expressions for the decay width are derived for resonances with arbitrary spin and parity. Contributions of the various terms in the transition matrix element are compared and relevance of spin-parity and the resonance mass is discussed. Explicit algebraic expressions are cited for spin <5/2 resonances. The results can be used in models of dielectron production in elementary reactions and heavy ion collisions.     

Complex mixing of baryon resonances

We employ the Wigner-Weisskopf method for a simultaneous treatment of decays, mass splittings and mixings of baryon resonances. Complex mixing matrices naturally arise in this context. Most of the amplitudes at resonance become also complex now and we make predictions for their phases. In spite of the doubling of the number of parameters in the mixing matrices the well0known discrepancies between decay and spectrum analyses still persist.     

Phase motion of baryon resonances

A novel technique to probe the resonant structure of a partial-wave amplitude is proposed and applied to data on photoproduction of baryon resonances.     

Search for diquark substructures in charmed baryon spectroscopy

We suggest that the present experimental evidence for two Λ_c⁺ mass levels may have a deep physical significance and can be taken as the first hint of (cu) and (cd) diquark substructures within the baryon.     

Belle实验发现新粲重子存在的迹象

粲重子是含有粲夸克的一类重子。粲重子存在很丰富的激发态,粲重子谱的研究对理解轻夸克在含重夸克系统中的动力学行为,以及检验重夸克对称性和轻夸克手征对称性具有重要意义。Λ⁺_c是质量最轻的粲重子,它是由一个粲夸克、一个上夸克和一个下夸克构成的同位旋单态。最近,日本的Belle实验利用在Υ(4S)中心质量采集的772×10⁶对B相似文献   

On the lifetime of charged charmed particles first direct observation of a charmed baryon decay

Two new examples of production by neutrinos and subsequent decay of charged charmed hadrons are reported. Together with two similar events reported previously they show that the lifetime of charged charmed particles is in the neighbourhood of 5 × 10^?13 s, as expected from current theoretical models. One of the new events is identified as a baryon λ_c⁺ of mass 2.295 ± 0.015 GeV/c² which undergoes the decay process λ_c⁺ → pπ⁺K^? with a proper decay time (7.3 ± 0.1) × 10^?13 s.     

Evidence for charmed baryon “elastic” production in neutrino reactions at the CERN SPS

Evidence for charmed baryon “elastic” production is found in a sample of 55 000 charged-current neutrino interactions in the bubble chamber Gargamelle exposed to the SPS wide-band neutrino beam. The product of the average cross section times the branching ratio into modes including a Λ⁰ or a $\text{K}$⁰p system is found to be α·B=(14.3 ± 7.4) × 10^?40 cm² for ν+n reactions and α · B<3.3×10^?40 cm² (90% CL) for ν+p reactions.     

Charmed baryon heavy-quark resonances with symmetry

We study charmed baryon resonances that are generated dynamically from a coupled-channel unitary approach that implements heavy-quark symmetry. Some states can already be identified with experimental observations, such as Ac（2595）, Ac（2660）, Ec（2902） or Ac（2941）, while others need a compilation of more experimental data as well as an extension of the model to include higher order contributions. We also compare our model to previous SU（4） schemes.     

Charmed baryon resonances with heavy-quark symmetry

We study charmed baryon resonances that are generated dynamically from a coupled-channel unitary approach that implements heavy-quark symmetry. Some states can already be identified with exper-imental observations, such as Λ_c(2595), Λ_c(2660), Σ_c(2902) or Λ_c(2941), while others need a compilation of more experimental data as well as an extension of the model to include higher order contributions. We also compare our model to previous SU(4) schemes.